Centrifugal compressor cooling

ABSTRACT

Systems, apparatuses and methods (“utilities”) for use in “internally” cooling an centrifugal compressor of a gas turbine engine so as to approximate isothermal compression and thereby increase the power and/or efficiency of the engine. In one arrangement, a centrifugal housing having fluid or coolant paths is provided to absorb heat or thermal energy generated while compressing intake air.

CROSS REFERENCE

The present application claims the benefit of U.S. Provisional PatentApplication No. 62/432,435 having a filing date of Dec. 9, 2016, theentire contents of which is incorporated herein by reference.

FIELD

The present disclosure is directed toward centrifugal compressors. Morespecifically, the present disclosure is directed towards systems andmethods for cooling a centrifugal or radial compressor of a gas turbineengine to reduce the temperature rise of air passing through thecompressor and thereby reduce the power required by the compressor.

BACKGROUND

A gas turbine engine extracts energy from a flow of hot gas that isproduced by the combustion of gaseous or liquid fuel with compressedair. In its basic form, a gas turbine engine employs a rotary aircompressor driven by a turbine with a combustion chamber disposedbetween the compressor and the turbine.

Principles of thermodynamics teach that when the temperature of thegases entering the turbine exceeds that entering the compressor, theturbine can deliver more power than the compressor consumes. In thisregard, the engine can produce a net power output contingent upon othercriteria being met. The efficiency with which the engine convertsthermal energy into mechanical energy depends on many factors includingcompressor and turbine efficiencies, temperature and pressure levels,and the presence or absence of enhancements such as regeneration andcompressor air stream cooling (intercooling). The power produced isproportional to the efficiency as well as the mass flow rates of air andfuel. Turboshaft engines deliver mechanical power through a rotatingoutput shaft. Turbojet or turbofan engines require only enough turbinepower to operate the compressor (with or without a fan) and the excessfluid power is available in the form of jet thrust.

Conventional gas turbine engines operate approximately according to theideal “Gas Turbine” or “Brayton” cycle which, by definition, embodiesreversible adiabatic (without heat transfer) compression of atmosphericair, addition of heat at constant pressure, reversible adiabaticexpansion through a turbine back to atmospheric pressure, and finallyexhausting to the atmosphere. Deviations from the ideal cycle (e.g.,irreversibilities) arise due fluid friction and turbulence,inefficiencies in compressors and turbines, combustion heat loss, andthe like.

The Ericsson Cycle patented in 1830 embodies constant pressureregeneration, isothermal compression, and isothermal expansion (reheat),but proposes no means of accomplishing either isothermal compression orexpansion. The ideal Ericsson Cycle has “Carnot” efficiency (classicalthermodynamics proves that no ideal heat engine operating between givensource and sink temperatures can exceed Carnot Cycle efficiency). Whilethe visionary scientists of the nineteenth century, Nicolas Carnot,James Joule, Lord Kelvin, Rudolf Clausius, and Ludwig Boltzman whodeveloped the new branch of science (i.e., Thermodynamics) as well asmodern engineers have recognized the benefits of isothermal compressionand turbine reheat, no known practical method of achieving orapproximating approximate isothermal compression (or expansion) has beenperfected.

One attempt to remove compression heat from the engine (“externalintercooling”) diverts air out of each stage of an axial compressor,passes the air through a separate heat exchanger/radiator, andre-injects the cooled air into the inlet of the next compressor stage.However, the circuitous piping and multiple changes in flow directioncould defeat much, or all of any thermodynamic advantage of externalintercooling.

Another disadvantage of external-intercooling is how the increasedcomplexity of such systems significantly increases the weight of aturbine engine. This is especially relevant to aircraft applicationswhere turbine engines are often utilized due to their high power toweight ratio. That is, in most cases, gas turbine engines areconsiderably smaller and lighter than reciprocating engines of the samepower rating. For this reason, turboshaft engines are used to poweralmost all modern helicopters. However, incorporation of externalintercoolers into turbine engines would result in a significant additionof weight which would more than offset any power gain benefits for suchapplications.

SUMMARY

Provided herein are systems and methods (i.e., utilities) that implementwhat is termed “Approximated Isothermal Compression” (AIC) in acentrifugal compressor of a gas turbine engine. AIC provides significantimprovements in heat rate and power (10-25% depending on turbine design)by implementing centrifugal or radial compressor cooling that lowers thework required by a turbine engine to compress air. In various utilities,a liquid coolant is supplied to a compressor housing that houses acentrifugal compressor. In various aspects, which may be utilizedtogether and/or independently, the liquid coolant is the fuel utilizedby the combustor of the turbine engine. Use of the fuel as the coolantmakes the utilities well suited for use in aircraft applications as theaircraft are not required to carry separate coolant and/or complexplumbing, pumps and radiators to reject heat from the coolant.

Disclosed herein are various apparatuses, systems and methods to achievewhat will be referred to herein as “external intercooling”. Externalintercooling is the cooling of a centrifugal compressor airstreamwithout disrupting the normal flow path of the airstream through thecentrifugal compressor. Such external cooling can expel much of thecompression heat in the centrifugal compressor to approximate isothermalcompression in the centrifugal compressor stage and thereby reduce theconsumption of power by the centrifugal compressor. That is, variousaspects of the presented inventions are directed to practical andeffective means of expelling much of the compression heat in order toreduce the consumption of power by the compressor. While cooling of thecentrifugal compressor reduces the compressor discharge temperature,such cooling can cause an increase in the fuel flow rate needed tomaintain the turbine inlet temperature at its set value, the incrementalincrease in the required combustion heat is the same as the incrementaldecrease in compressor specific work. Thus, the turbine net specificwork (i.e., total turbine specific work minus compressor specific work)increases by that same amount (i.e., the output power increases byexactly the same amount as the increase in combustion heat rate). Asefficiency is given by net-power/combustion-heat-rate, efficiencyactually increases because the same increment is added to the numeratorand denominator of a fraction less than 1.0 (i.e., this causes anincrease in the value of the fraction).

One of the utilities disclosed herein includes specially designedcompressor impellor housing that absorbs thermal energy which can thenbe transferred away from the airflow through the compressor. Theapparatus generally includes an annular compressor housing includinginside and outside surfaces, and inlet and outlet ends, such that airgenerally moves in an air flow direction from the inlet end towards theoutlet end. A sidewall extends between the inlet and outlet. Formedwithin the sidewall are one or more fluid path that allow forcirculating fluid (i.e., coolant) though the housing. In onearrangement, fuel of a gas turbine engine using the compressor housingis used as the coolant. This arrangement allows for both removing heatfrom the compressed air, thereby reducing the power needed by thecompressor to compress the intake air, and preheating the fuel prior tocombustion. In another arrangement, the coolant may be a closed systemwhere coolant is circulated through the compressor housing and the heatabsorbed from the coolant is rejected using, for example, a radiator. Inthis arrangement, the heated coolant may be utilized to preheat the fuelusing, for example, a separate heat exchanger.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a perspective view of a gas turbine engine.

FIG. 2 shows a side view of the engine of FIG. 1.

FIG. 3 shows an end view of the engine of FIG. 1.

FIG. 4 shows an exploded view of an axial compressor assembly.

FIG. 5 shows an exploded view of a portion of a centrifugal compressorassembly.

FIG. 6A shows a perspective view of an internally cooled centrifugalcompressor housing.

FIG. 6B shows a side view of an internally cooled centrifugal compressorhousing.

FIG. 6C shows a cross-sectional view of an internally cooled centrifugalcompressor housing.

FIG. 7 shows an internally cooled compressor housing used for anaircraft application.

FIG. 8 shows an internally cooled compressor housing used with anexternal cooling system.

DETAILED DESCRIPTION

Reference will now be made to the accompanying drawings, which assist inillustrating the pertinent features of the various novel aspects of thepresent disclosure. Although described primarily with respect tocompressor cooling systems, apparatuses and methods (i.e., utilities)that may or may not be combined with recuperation and used with aturbine engine (e.g., in aircraft applications), aspects of theutilities are applicable to centrifugal compressors that may be utilizedfor gas compression applications such as gas pipeline compressors. Inthis regard, the following description is presented for purposes ofillustration and description. Furthermore, the description is notintended to limit the inventive aspects to the forms disclosed herein.Consequently, variations and modifications commensurate with thefollowing disclosures are within the scope of the present inventiveaspects.

The presented centrifugal compressor cooling systems and methodsdiscussed herein may be utilized with a variety of different gas turbineengines. The present description describes the centrifugal compressorcooling utilities in relation to the Rolls-Royce Model 250 family ofengines (US military designation T63). However, discussion of thepresented utilities with the Model 250 engine is presented by way ofillustration and not by way of limitation. The presented utilities maybe unitized with various gas turbine engines including other aircraftengines and ground based engines as well as other centrifugalcompressors.

The Model 250 engine 10, as schematically shown in the perspective, sideand front views of FIGS. 1-3, utilizes what is sometimes referred to asa “trombone” engine configuration whereby air enters the intake of anaxial compressor 20 and passes through an axially aligned centrifugalcompressor 22 in a conventional fashion, but whereby compressed airleaving the compressors 20, 22 is ducted rearwards around the turbinesystem via external air ducts 24. That is, unlike most other turboshaftengines, the compressors 20 and 22, combustion chamber or combustor 30and turbine section or stage 40 are not provided in an inlineconfiguration with the compressors at the front and the turbine at therear where compressed air flows axially through the engine. Rather, inthe Model 250 engines, the engine air from the forward compressor 20 ischanneled through the external compressed air ducts 24 on each side ofthe engine 10 to the combustor 30 located at the rear of the engine. Theexhaust gases from the combustor 30 then pass into a turbine stage 40located intermediate the combustor 30 and the compressor 20. The exhaustgases are exhausted mid-engine in a radial direction from the turbineaxis A-A of the engine, through two exhaust ducts 42. A power take-offshaft 44 connects the power turbine of the turbine stage to a compactreduction gearbox (not shown) located inboard between the compressor andthe exhaust/power turbine system.

Gas turbine engines are described thermodynamically by the idealizedBrayton cycle, in which air is compressed isentropically, combustionoccurs at constant pressure, and expansion over the turbine occursisentropically back to the starting pressure. In practice, friction andturbulence cause non-isentropic compression. Specifically, thecompressor tends to deliver compressed air at a temperature that ishigher than ideal. Furthermore, pressure losses in the air intake,combustor and exhaust reduce the expansion available to provide usefulwork. By some estimates, up to half of the power produced by the enginegoes to powering the compressor.

FIG. 4 illustrates an exploded view of the axial compressor 20. Broadly,the compressor 20 may include a rotor structure 109 and a statorstructure 103. The rotor structure 109 includes a rotating shaft 110that extends through the engine 10 to the turbine stage 40. The rotatingshaft 110 include multiple attached rotor sections 112 spaced along thelength of the rotating shaft 110, each of which include a series or setof rotor blades 113 extending away from the rotating shaft 110. Thestator structure 103 also include a stator housing or axial compressorhousing 100 having inside and outside surfaces 107, 120, inlet andoutlet ends 104, 108 and a central axis (not shown) running through thecenter of the axial compressor housing 100. As seen, the axialcompressor housing 100 may be divided into first and second halves 115,116. A plurality of stator rows or sections 102 may be disposed on theinside surface 107, each of which may include a series or set of statorvanes or blades 114.

In assembly, the first and second halves 115, 116 of the housing may beinterconnected together (e.g., via bolts and apertures, not labeled)such that the stator casing 100 surrounds the shaft 110 and rotorsections 112 and a longitudinal axis (not shown) of the rotating shaft110 is coincident with the central axis of the axial compressor housing100. At this point, the stator sections 102 and rotor sections 112 mayalternate and the rotor sections 112 may be operable to rotate in thespaces between the stator sections 102. The angles of each of the statorand rotor sections 102, 112 may also alternate. Furthermore, the variousstator and rotor sections 102, 112 may have different spacing (e.g.,blade density) as well as different angles from the previous rows ofblades.

As further shown in FIG. 4, the outlet end 108 of the axial compressorhousing defines a flange having a plurality of bolt apertures. Thisallows the axial compressor casing to be firmly attached to an inletflange 56 of an impellor housing 50 of the centrifugal compressor 22. Inthis regard, air compressed by the axial compressor 20 passes out of theoutlet end 108 and into the inlet end of the centrifugal compressor 22.A portion of the centrifugal compressor 22 is illustrated in FIG. 5 asshown, the centrifugal compressor 22 includes an impellor 52 having aplurality of vanes. The impeller 52 is interconnected to the shaft 110and, in the present embodiment, co-rotates with the rotor blades of theaxial compressor. When assembled, the impeller 52 is encased within thehousing 50. In operation, the impeller 52 further compresses the airreceived from the axial compressor. That is, during operations the rotorblades 113 turn relative to the stator blades 114, air advances from theinlet end 104 of the stator casing 100 through the multiple rows (e.g.,stages) of stator blades 114 and rotor blades 113 and discharges throughthe compressor outlet end 108 into the centrifugal compressor 22 whereit is further compressed by the impellor 52 of the centrifugalcompressor 22 after which it is discharged through a diffuser into theair ducts 24. See FIG. 4 4. As the air advances through the axialcompressor 20 and centrifugal compressor 22, the air may be compressedfrom ambient pressure to over 100 psi. However, the compression pressuremay vary between different engines. In addition to being compressed, thefriction of the blades (e.g., rotor blades and impellor vanes) rotatingand air passing over the blades applies significant heat to the air. Forinstance, air entering at ambient temperature of approximately 518.67° Rmay be heated to a temperature over 1000° R. The temperature increasemay vary between different engines.

The increase in the temperature of the air as it passes through thecompressors 20 and 22 results in the air expanding and thus workingagainst its compression. Stated otherwise, the addition of heat to thecompressed air is parasitic and requires that the engine supply morecompression power to achieve the desired output pressure. Accordingly,utilities disclosed herein are directed to reducing the temperature gainof air flowing through the centrifugal compressor to reduce compressionpower requirements and thereby increase the available shaft output powerof the engine.

Aspects of the present disclosure are based on the realization thatsignificant reduction in the temperature rise of the compressed intakeair may be achieved via cooling the centrifugal compressor housing. Invarious arrangements near isothermal compression may be achieved throughthe centrifugal compressor via centrifugal compressor housing coolingwhich reduces the power requirements of the compressor improving overallefficiency of the engine. Along these lines, it is been determined thatthe centrifugal compressor housing 50 may be formed by a plurality ofinternal fluid paths through which coolant may be circulated. Thecoolant passing through the compressor housing 50 removes thermal energyfrom the compressor housing lowering its temperature and thereby permitsheat exchange between the hot intake air passing through the interior ofthe cooled housing.

FIGS. 6A, 6B and 6C illustrated perspective, side, and cross-sectionalviews, respectively, of an internally cooled centrifugal compressorhousing 50. As shown, the compressor housing 50 includes an annularinlet flange 56 and an annular outlet flange 58 both of which include aplurality of apertures for attachment to mating components of a gasturbine engine or other compressor system. An annular sidewall 60extends between the inlet flange 56 and the outlet flange 58. The inletflange 56 defines a central inlet or aperture for receiving inlet air(e.g., upstream gas) and the outlet flange defines a central outletaperture for outputting outlet air (e.g., downstream gas) compressed byan impeller encased within the housing 50. As shown, the inlet aperturehas a first diameter that is typically smaller than a second diameter ofthe outlet aperture. Accordingly, an inside surface 62 of the sidewalltransitions between the first smaller diameter and the second largerdiameter of the housing 50. The curvature of the inside surface 62 istypically configured to substantially match the shape of the impellerencased within the housing 50. That is, the inside surface 62 issubstantially similar in shape to a surface defined by rotation of theimpeller 52. It will be appreciated that the exact shape of the insidesurface 62 may be varied based on the configuration of the impeller 52.An outside surface 64 of the sidewall 60 is spaced from the insidesurface and may, but need not, generally correspond to the shape of theinside surface 62.

Within the sidewall 60 between the inside surface 62 an outside surface64 are plurality of fluid passages or fluid paths 70. The fluid paths 70extends between a first inlet/outlet port 72 and a second inlet/outletport 74 formed into the outside surface 64 of the housing 50.Accordingly, appropriate fluid conduits may be connected to the ports72, 74 to circulate fluid through the housing 50 while the impeller isoperating therein. Such fluid flow permits the removal of thermal energyfrom the housing which in turn reduces the temperature of the air beingcompressed by the impeller. In a further embodiment, surface featuresmay be added to the interior surface of the housing (e.g., grooves,ridges, vanes, etc.) to increase the surface area of the interiorsurface and thus increase the heat exchange of the cooled housing.

The exemplary fluid path 70 is a spiraled or roughly helical fluid paththat extends multiple rotations around the center axis of the housing.Though using the word helical, it will be appreciated that the radiusand or pitch of the spiral may be varied throughout the sidewall. In anembodiment utilizing a spiraled or helical type fluid path, the fluidpath may be a single passage or a manifold of passages that extendsbetween the first and second ports 72, 74. As shown in FIG. 6C, thecross-sectional shape of the singular spiral fluid path or passage isvaried depending on its location within the sidewall. The size and shapeof the fluid path may be selected to provide desired thermal propertiesand/or to facilitate manufacture. Further, the shape (e.g.,cross-sectional, diameter, etc.) of the fluid path(s) may vary alongtheir length. Though illustrated utilizing a single continuous spiralfluid path, it will be appreciated that fluid paths of differentconfigurations may be utilized within the sidewall. For instance,annular manifolds may be defined proximate to the inlet and outletflanges which are connected by a plurality of fluid paths that flowtherebetween. In such an arrangement, the fluid paths may define a heatexchanger that is of the crossflow variety and/or counterflow variety.What is important is that the cooling fluid may be circulated betweenthe inlet and outlet ports and along the length of the sidewall toremove thermal energy from the housing. It will be further appreciatedthat various pumps may be included to circulate the fluid through thehousing. In some embodiments, the heated fluid may be directed to anexternal heat exchanger or radiator (not shown) where the heat extractedfrom the compressor housing may be rejected, for example, into theatmosphere or another fluid or process.

In an embodiment well suited for use in aircraft applications, the firstport 72 may be connected to the fuel tank of the aircraft via a firstconduit 82. See FIG. 7. In such an arrangement, the second port 74 maybe connected to the combustor via a second conduit 84. In thisembodiment, the fuel supply of the aircraft essentially serves as thecoolant for the centrifugal compressor just prior to combustion. A dualbenefit can be achieved by using the fuel as a coolant and preheatingthe fuel to a more thermodynamically favorable combustion temperaturecan thus be achieved. This typically requires that the fuel coolant beprovided under a predetermined pressure. This embodiment reduces theneed of having a separate coolant cooling system. That is, no pump orradiators are required to reject heat from the coolant used to cool thecompressor housing. Rather, the heated fuel is simply burned in thecombustor. Heat rejection via a separate coolant cooling system may bereduced or eliminated.

In another embodiment, a secondary coolant loop is incorporated. SeeFIG. 8. In this embodiment, a pump 80 is incorporated to pump coolant inthrough a coolant loop 90 through the compressor housing 50 and one ormore heat rejection devices. In one embodiment, the coolant loop 90passes through a heat exchanger 92 to preheat fuel the passes throughthe heat exchanger 92. Additionally or alternatively, the coolant loop90 may also incorporate a radiator 94 to reject heat from the coolantafter it has passed through the compressor housing 50. In such anembodiment, the benefit of heating the fuel is realized and the heatexchange between the coolant and the fuel facilitates heat rejectionfrom the coolant.

The impeller housing 50 including the internal fluid path(s) 60 may, inone embodiment, be formed using a three-dimensional printing technique.For instance, the impellor housing may be formed in a direct metal lasersintering (DMLS) process. DMLS is an additive manufacturing techniquethat uses a carbon dioxide laser fired into a magnesium substrate tosinter powdered material (typically metal), aiming the laserautomatically at points in space defined by a 3D model, binding thematerial together to create a solid structure. Thus, any 3D model may beformed in a DMLS process. Alloys used in the process include, withoutlimitation, 17-4 and 15-5 stainless steel, maraging steel, cobaltchromium, inconel 625 and 718, and titanium Ti6A14V. It will beappreciated that any appropriate printing process may be utilized.Alternatively, the impeller housing may be machined where, for example,the inner surface is connected (e.g., bonded, welded, etc.) to thesidewall containing milled fluid paths.

The ability to provide cooling to the impellor housing can significantlyreduce the compressor air outlet temperature. That is, compressed airtemperature rise may be significantly reduced in comparison to thetemperature rise in a conventional turbine engine. This reducedcompressor output temperature is a modification of the basic gas turbineBrayton cycle. In a theoretical limit, compression may be done atconstant temperature or ‘isothermal’ compression with the remainder ofthe cycle being the same as the Brayton cycle—constant pressurecombustion and isentropic expansion. This modified cycle is referred toherein as the ‘Approximated Isothermal Compression’ AIC cycle, whichutilizes isothermal or reduced temperature rise compression.

To improve engine efficiency and power output, any appropriate manner ofachieving regeneration may be included along with the apparatuses andmethods disclosed herein for cooling a centrifugal compressor and/or theairstream flowing therethrough. Regeneration is the use of a heatexchanger to transfer heat from an engine exhaust stream to thecompressor discharge air (thus preheating the compressor discharge air)in a turbine engine such that less fuel energy is required to achievethe required turbine inlet temperature for the compressed air. Byrecovering some of the energy usually lost as waste heat, a regeneratorcan make a gas turbine engine significantly more efficient. Such asystem is disclosed in U.S. patent application Ser. No. 12/650,857,entitled “Recuperator for Gas Turbine Engines,” which in incorporatedherein by reference.

What is claimed is:
 1. A housing for a centrifugal or radial compressorof a gas turbine engine, comprising: an annular inlet flange forupstream gas connection having a central inlet aperture, said annularinlet flange having a first diameter; an annular outlet flange fordownstream gas connection having a central outlet aperture, said annularoutlet flange having a second diameter greater than said first diameterand wherein a reference line passing between the centers of said centralinlet aperture and said central outlet aperture defines a centerlineaxis of the housing; an annular sidewall extending between said annularinlet flange and said annular outlet flange, said sidewall including: anannular inside surface that transitions between said first diameter andsaid second diameter, wherein said annular inside surface is configuredto receive a centrifugal impellor of the gas turbine engine; an outsidesurface spaced from said inside surface; and a fluid path disposedwithin said sidewall between said inside surface and said outsidesurface, wherein said fluid path extends between a first fluid port insaid outside surface proximate to said annular inlet flange and a secondfluid port in said outside surface proximate to said annular outletflange.
 2. The housing of claim 1, wherein said annular inside surfacecomprises a curved surface between said annular inlet flange and saidannular outlet flange.
 3. The housing of claim 1, wherein said annularinside surface is complementarily shaped to an outside surface definedby rotation of the centrifugal impellor.
 4. The housing of claim 1,wherein said fluid path comprises a spiral or helical fluid path.
 5. Thehousing of claim 4, wherein said helical fluid path between said firstfluid port and said second fluid port comprises at least one fullrotation about said centerline axis.
 6. The housing of claim 5, whereinsaid helical fluid path comprises at least two full rotations about saidcenterline axis.
 7. The housing of claim 1, wherein said fluid pathcomprises a plurality of cooling passages within said sidewall.
 8. Thehousing of claim 7, wherein said cooling passages form one of aparallel-flow, cross-flow, a counter-flow, or a cross-counter-flowpattern between said first fluid port and said second fluid port.
 9. Thehousing of claim 1, wherein said annular inside surface furthercomprises groves ridges or other geometries that increase a surface areaof said annular inside surface.
 10. A gas turbine engine comprising: acentrifugal impellor to compress intake air; a combustor to combust fuelwith compressed intake air; a turbine in flow communication with saidcombustor; and a compressor housing surrounding said centrifugalcompressor having: an annular sidewall extending between an annularinlet flange having a first diameter and an annular outlet flange havinga larger second diameter, said sidewall including: an annular insidesurface that transitions between said first diameter and said seconddiameter, wherein said annular inside surface is configured to receivesaid centrifugal impellor; an outside surface spaced from said insidesurface; and a fluid path disposed within said sidewall between saidinside surface and said outside surface, wherein said fluid path extendsbetween a first fluid port in said outside surface proximate to saidannular inlet flange and a second fluid port in said outside surfaceproximate to said annular outlet flange.
 11. The gas turbine engine ofclaim 10, further comprising: a fuel tank fluidly connected to saidcombustor via said fluid path.
 12. The gas turbine engine of claim 11,further comprising: a first fluid conduit extending between said fueltank and one of said first fluid port and said second fluid port and asecond fluid conduit extending between the other of said first fluidport and said second fluid port and said combustor.
 13. The gas turbineengine of claim 11, further comprising: a pump for pumping fuel throughsaid fluid path at a predetermined pressure.
 14. The gas turbine engineof claim 10, wherein said fluid path comprises a plurality of coolingpassages within said sidewall.
 15. The gas turbine engine of claim 14,wherein said fluid path comprises one of: a helical path; a cross-flowpath; a counter-cross-flow path; a parallel path and a counter-flowpath.
 16. The gas turbine engine of claim 14, further comprising: acoolant loop connected to the first port and the second port, wherein apump pumps coolant through the coolant loop and through the fluid path.17. The gas turbine engine of claim 17, wherein the coolant loop furthercomprises: a heat exchanger connected to a a fuel pathway, wherein fuelremoves thermal energy from said coolant in said coolant loop.
 18. Thegas turbine engine of claim 18, wherein the coolant loop furthercomprises: a radiator for rejecting heat from the coolant.
 19. A methodfor use with a centrifugal compressor of a gas turbine engine,comprising: rotating an impellor within a compressor housing to compressintake air between an inlet of the housing and an outlet of the housing;circulating fluid through at least a first passage disposed within asidewall of the compressor housing to remove thermal energy from thehousing and air compressed by the impellor.
 20. The method of claim 20,wherein circulating fluid comprises: circulating fuel for use in acombustor of the gas turbine engine through the fluid path, wherein thefuel is circulated under a predetermined pressure.